The instant invention relates to privacy filters for electronic display devices, such as personal digital assistants (PDA""s) and laptops, and more particularly to a privacy filter that makes use of holographic images to block the view of unwanted onlookers, but yet allow the operator to have an unobstructed view of the display screen.
Privacy filters for electronic display devices are well known in the electronic and optical arts. The growing use of electronic devices in public areas has driven a need in the industry to try to develop products which will protect private and confidential information from the view of unwanted onlookers, but yet allow the intended viewer, i.e. the user, to have a substantially unrestricted view of the display.
One important area of use for privacy filters is in the travel sector. Business travelers on planes and trains, etc., have an inherent need to be able to work while traveling. For the most part, almost every business traveler has a laptop or PDA device that when in use, will be generally visible to anyone sitting next to them, or somewhere behind them. The ever improving clarity and brightness of the displays of such devices makes the problem even worse as persons sitting a substantial distance away can view the substance of whatever is displayed on the device.
Another popular venue of use for privacy filters is in the medical field where confidential patient information is displayed on hospital computer screens. It is important that doctors, hospitals and other medical facilities make use of some type of privacy device on the screens of their computers to insure that other patients and unintended hospital staff cannot see patient information displayed on such computer screens. These types of computers typically have a conventional cathode ray tube (CRT) display, although, the use of Liquid Crystal Display (LCD) screens is growing more popular and affordable. LCD screens are the same type of screens that are used in laptop and PDA devices.
Privacy screens are also used in schools and libraries where a plurality of computers might be grouped together in a common area. Individuals using computers in these public circumstances may also want to prevent others from viewing confidential information.
In general, the object of a privacy filter is to prevent someone who is not directly in front of the display screen from being able to read the information displayed on the screen. Typically, the existing privacy filters provide about a 60 degree field of view directly in front of the display. The remaining 60 degree fields of view to the right and to the left of central field of view are blocked by one or more techniques of diffracting or blocking light waves. One known technique of blocking light is by the use of louvered echelon lenses formed on a flexible plastic sheet. The lenses are arranged at particular angles such that when the flexible plastic sheet is overlayed onto a display, a viewer directly in front of the screen can view the screen without substantial distortion. However, as the field of view is shifted to the left and right of the center, the screen appears to be black, as the louvered echelon lenses entirely block light from exiting the filter in those angled directions. This type of filter can be constructed in any size or shape. However, the one drawback is the cost of such filters. The cost of a filter for a single 12 inch laptop computer screen can exceed $85 retail. 15 inch versions of this type of filter can exceed $120. The purchase of quantities of such filters for schools and government bodies is almost prohibitive.
Another type of privacy filter does not entirely block the light from the side angles but rather diffuses or diffracts the light to a sufficient extent to blur the image displayed. This technique is effective for use with text displays as the individual words are unreadable from the side angles.
Still further, other types of filters make use of parallel grids or agglomerates of small particles suspended in a plastic matrix to diffuse or diffract light in a desired manner.
While each of the existing prior art privacy filters is effective for its intended purpose, there is nevertheless a continuing need in the industry for newer and less expensive products which will allow more widespread use and adoption.
The instant invention provides a privacy filter that makes use of holographic images to block the view of the display screen from side, front and rear angles, but yet allows the user to view the display screen from directly in front thereof, i.e. within the central field of view. More specifically, a privacy filter for use on an electronic display screen, such as a PDA display screen or a laptop display screen, is constructed using holographic imaging technology. The privacy filter consists of a flexible, optically clear photopolymer film having a plurality of holographic images formed thereon. The key aspect of the present disclosure is constructing the master holographic images by imaging the master holographic recording plates at a severe side angle xe2x80x9coff anglexe2x80x9d of about 60 degrees from center. Conventional hologram images are recorded at a standard angle of 45 degrees from center and are visible within the central field of view. By shooting the hologram images at this xe2x80x9coff anglexe2x80x9d, the resulting hologram is not visible to a person within the central field of view looking directly (perpendicularly) at the resulting holographic film, but rather the viewable image of the hologram is shifted to the right or left depending from which side the image is recorded. This means that the holograms are now visible within the remaining fields of view to the right and to the left of center. Creation of the holograms in this manner creates an effective visibility blocking tool for use in the context of a privacy filter. Unwanted onlookers attempting to view the display screen from the sides, the front or the back are presented with a holographic image rather than a view of the display.
In its most basic form, the privacy screen comprises a single flexible sheet of photopolymer film having at least one holographic image formed therein. Since the view of the holographic images is shifted in the direction of the recording angle, it would normally be necessary to image two separate images, one from the right and one from the left, to achieve the desired effect of blocking from both sides. This, however, would require the use of two overlayed sheets of photopolymer film. It has been found as part of the invention, that if the holographic image is recorded at a 60 degree angle from the top center of the plate rather than from the left or right side, the resulting holographic image is visible from both the left side, right side, and the front. It was also found in the course of development that larger holograms tend only to be partially visible, depending on the angle at which they are viewed. Accordingly, in the preferred form of the invention, the photopolymer film is imaged with a plurality of individual, smaller holographic images that are arranged in a pattern across the surface of the film. By using a plurality of separate holographic images, each image independently becomes fully visible within the side privacy fields of view, i.e. the images all xe2x80x9cpopxe2x80x9d into view simultaneously, rather than seeing a gradual appearance of the image from one side to the other.
The privacy filter further preferably includes an layer of adherent material attached to the back of the photopolymer film to provide a means of adhering the film to a display screen. One type of adherent material is a layer of static cling vinyl which is effective for adhering the film to glass surface, such as found on many PDA screens and CRT screens. Another type of adherent material is a layer of pressure sensitive adhesive, such as used on self sticking post notes, which is effective for adhering the film to non-glass screens such as used in LCD laptops screens and other types of PDA""s.
Still further, the privacy filter preferably includes a protective xe2x80x9canti-scratchxe2x80x9d coating on the upper surface thereof, which protects the film and increases the life of the product.
In the manufacturing process of the master plates, each individual holographic image is separately recorded at the critical xe2x80x9coff anglexe2x80x9d and then the individual master recording plates are assembled together to form an array of individual plates. This array is then reproduced or xe2x80x9ccopiedxe2x80x9d to form a larger format master plate (2nd generation) which is then used for exposure of the photopolymer film. Preferably, the 1st generation master plates are imaged without any object or pattern such that the holographic effect is simply the appearance of a plain greenish shade. When the array of 1st generation master plates are copied, a mask with a two-dimensional stencil pattern is overlayed on the array to mask out the seems of the tiles and to create a repeating pattern in the holographic image. This 2-D pattern is then what becomes visible as the holographic images when the photopolymer film is exposed. Alternative methods of recording the holographic images include the use of blocking plates to remove ghosting effects, and the use of mask overlays in the creation of the 1st generation master plates.
As briefly, discussed above, an alternative embodiment of the privacy filter makes use of two separate layers of photopolymer film overlayed to form a composite filter. In this case, each of photopolymer films are exposed with a master plate imaged from the extreme right side or the extreme left side. The resulting holographic images are very clearly seen from the left and right sides. The manner of constructing the holographic master plates is the same as discussed above, but must be carried out for each set of left and right images. Likewise, there are two processes of exposure and two sheets of photopolymer film.
The holographic images can also comprise images of three-dimensional (3-D) objects rather than 2-D patterns.
Accordingly, among the objects of the instant invention are: the provision of a privacy filter that prevents unwanted viewers from seeing the screen of an electronic device outside of a central field of view; the provision of a holographic privacy filter that displays holographic images to unwanted viewers outside of the central field of view; the provision of a holographic privacy filter for a PDA device; the provision of a privacy filter for a laptop computer screen; the provision of a privacy filter for CRT screens; the provision of holographic privacy filter that simultaneously displays a plurality of individually created holographic images within the obstructed fields of view; the provision of a holographic privacy filter that is inexpensive to manufacture and which can be mass produced at a low cost using known manufacturing methods; the provision of a method of constructing a holographic privacy filter; the provision of method of assembling a plurality of individual holographic tiles together to form a holographic privacy filter; the provision of such a method wherein a plurality of holographic tiles are assembled together to form a PDA-sized holographic privacy filter; and the provision of such a method wherein a plurality of holographic tiles are assembled together to form a laptop or CRT sized privacy filter.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.